1. Field of the Invention
The present invention relates to a positive photosensitive composition suitable for use in microlithography processes such as the production of ULSIs or high-capacity microchips and in other photofabrication processes. More particularly, the invention relates to a positive photosensitive composition capable of forming a high-resolution pattern with a vacuum ultraviolet light having a wavelength of 193 nm or shorter.
2. Description of the Related Art
The degree of integration in integrated circuits is increasing more and more, and it has become necessary to form an ultrafine pattern having a line width of a quarter micrometer or smaller in the production of semiconductor substrates for ULSIs or the like. One of the known techniques for enhancing the fineness of such patterns is to use an exposure light having a shorter wavelength in resist pattern formation.
For example, in the production of semiconductor elements having an integration degree of up to 64 megabits, the i-line (365 nm) from a high-pressure mercury lamp has hitherto been used as an exposure light. Many compositions comprising a novolak resin and a naphthoquinonediazide compound as a photosensitive substance have been developed as positive resists for use with the exposure light, and have given sufficient results in forming patterns having line widths down to about 0.3 μm. On the other hand, in the production of semiconductor elements having an integration degree of 256 megabits or higher, KrF excimer laser light (248 nm) has been used as an exposure light in place of the i-line.
Furthermore, use of ArF excimer laser light (193 nm), which is an exposure light having an even shorter wavelength, and use of F2 excimer laser light (157 nm) for forming a pattern having a line width of 0.1 μm or smaller are recently being investigated for the purpose of producing semiconductor elements having an integration degree of 1 gigabit or higher.
With the use of such exposure lights having shorter wavelengths, the components of resist materials and the structures of compounds for use therein are changing considerably. For example, the related-art resists comprising a novolak resin and a naphthoquinonediazide compound have had the following problem. Since these resists show considerable absorption in a far ultraviolet region including 248 nm, the light is less apt to sufficiently reach the resist bottom. As a result, the resists have low sensitivity and give tapered patterns only.
In order to eliminate such problems, a so-called chemical amplification type resist has been developed. This resist is a composition which comprises a combination of: a resin, as the main component, which has a poly(hydroxystyrene) backbone showing reduced absorption in a 248 nm region and is protected by acid-dissociable groups; and a compound which generates an acid upon irradiation with far ultraviolet light (photo-acid generator). The chemical amplification type resist changes in solubility in a developing solution based on a decomposition reaction catalyzed by the acid generated in exposed areas, and can hence show high sensitivity and give high-resolution patterns.
However, in the case of using ArF excimer laser light (193 nm), even the chemical amplification type resist has been unable to have sufficient performances because compounds having aromatic groups intrinsically show considerable absorption in a wavelength region including 193 nm.
An improvement in the chemical amplification type resist has been attempted in order to overcome that problem. In this improvement, an acid-decomposable resin which has, incorporated in the polymer main chain or side chains thereof, alicyclic structures showing no absorption at 193 nm is used in place of the acid-decomposable resin comprising poly(hydroxystyrene) as the backbone.
However, it has been found that when F2 excimer laser light (157 nm) is used, even the alicyclic resin is insufficient in obtaining a desired pattern of 0.1 μm or finer because the resin shows considerable absorption in a 157 nm region. Under these circumstances, a resin having fluorine atoms (perfluorinated structure) incorporated therein was reported to have sufficient transparency at 157 nm, in Proc. SPIE., Vol. 3678, p. 13 (1999). Effective structures of such fluororesins are proposed in Proc. SPIE., Vol. 3999, p. 330 (2000), Proc. SPIE., Vol. 3999, p. 357 (2000), Proc. SPIE., Vol. 3999, p. 365 (2000), WO-00/17712, German Patent 1,005,466, Published U.S. Patent Application No. 2001/0,018,162 A2, etc.
However, the related-art resists containing a fluororesin have been desired to be further improved in sensitivity, line edge roughness diminution, and profile.